Electric furnace for producing silicon carbide



Sept. 18, 1928. 1,684,611

H. E. WHITE ELECTRIC FURNACE FOR PRODUCING SILICON CARBIDE Filed S ept.. 1925 s Sheets-Shet 1 glwcni'ol HRROLD E. WHYYE.

Sept. 18, 1928.

H. E. WHITE ELECTRIC FURNACE FOR PRODUCING SILICON CARBIDE ,Filed Sept. 1925 3 Sheets-Sheet HHROhD E... \NHVTE.

Sept. 18, 1-928. 1,684,611

H. E. WHITE ELECTRIC FURNACE FOR PRODUCING SILICON CARBIDE Filed Sept. 1925 3 Sheets-Sheet 3 Calcium Patented Sept. 18, 1928.

UNITED STATES PATENT OFFICE.

HAROLD E. WHITE, 0]? ANNISTON, ALABAMA, ASSIGNOR TO FEDERAL ABRASIVES COMPANY, OF BIRMINGHAM, ALABAMA, A CORPORATION OF ALABAMA.

ELECTRIC FURNACE FOR PRODUCING SILICON CARBIDE.

' Application filed September 4, 1925. Serial No. 54,562.

This invention relates to an improvement in electric furnace construction and particularly to the resistor type furnace suitable for use in the production of silicon carbide.

' The objects of this invention are to construct a rugged type of furnace which will or more, water-cooled copper tubes underneath the furnace for the return electrical circuit and for the most efficient useof the cooling water.

In the construction of piers or supports for the bottom of silicon carbide furnaces, it is common practice to use brick piers. I have found that reinforced concrete is much more satisfactory, because it withstands the strain of expanslon and contraction much better than brick piers. In the operation of silicon carbide furnaces a very high temperature is developed inside the furnace and this with.

the subsequent cooling causes considerable expansion and contraction. In addition to this feature the reinforced'concrete is a better supportfor the load of charge within the furnace.

The concrete heads are constructed with a taper from the base towards the top in such a manner to reduce the tendency to tip back from the pressure within the furnace. In addition to this feature, the ends are mounted on iron slides so that any expansion within the furnace will slide the head instead of tipping it. Also the copper tubes are not fastoned to the head, and accordingly are adapted to permit expansion of the furnace. In this manner a furnace is constructed with substantial supports and heads, as well as improved electrical characteristics.

My invention comprises the novel details of construction and arrangements of parts, which in their preferred embodiment only are illustrated in the accompanying drawings which form a part of this specification, and in which Fig. "l is a side View of one end of the fun nace which is broken away and has its other end shown in. vertical central cross-section with the charge omitted.

Fig. 2 is a plan View of Fig. 1, it being noted that in this view I have omitted the concrete and end packing poured about the right hand electrode.

F ig. 3 is a cross-sectional view of the furnace taken on the line 3-3 of Fig. 2.

F 4 is an end view of the furnace looking to the left, Fig. 2.

Fig. 5 is a detail View of one half section of a water-cooled electrode clamp.

Similar reference numerals refer to similar parts throughout the drawings.

In the embodiment of my invention illustrated in the drawings, I show the furnace comprising a pair of duplicate reinforced con: crete ends 1 which, as viewed in side elevation, are shown to flare outwardly and downwardly towards their bases both endwise and later ally so as to increase its bottom bearing and avoid a tendency to tip outwardly when subjected to expansion strains from the furnace. These ends 1 are free to slide endwise upon channel or rail supports 2 suitably anchored to the foundation 3 upon which the furnace rests. Between the heads I arrange a series of duplicate spaced reinforced-concrete cradies 4 each having an enlarged base 5 resting upon and anchored to the foundation 3 and having its upper brick supporting edge formed with a horizontal central face 6 merging into outwardly and upwardly inclined faces 7 which terminate at the top horizontal side ledges 8 disposed at each side of the furnace. The hearth support 9 of the furnace is laid upon these faces 6, 7 and 8 and is composed of bricks or blocks of. any suitable refractory material laid lengthwise along the said faces of the cradles. Upon the spaced hearth'supports 9 I lay the bricks or blocks 10 forming the hearth proper and these eX- tend lengthwise of the furnace so as to break joints on the centers of the crosswise bricks 9 lying on the faces 6, 7 and 8. Each face I of the cradles is provided with a notch 11 which align and receive the water-cooled copper tubes 12. These tubes pass freely through apertures 13 provided therefor in the ends it.

The ends 1 have in their inside faces a vertical recess or seat It which extends to the top of a transverse middle wall 15 and up along the spaced sides of the end to the top thereof. The open space providedabove the wall and between the spaced sides is adapted for the reception of the electrodes 16 which rest centrally upon the wall 15 and are disposed horizontally with their inner ends projecting substantially to the inside vertical plane of their respective end 1. The ends are provided with outwardly opening recesses 17 in the outer faces suitable to receive the holders 18 which are clamped about the outer ends of the electrodes. After the electrodes have been mounted in position, a composition 19 of coke, tar, pitch and sand is packed in around the inner end of the electrode between the sides of the furnace ends, filling the recess 14 and extending above the electrode to a level with the outside face of the wall 15. A concrete facing 20 is then poured about the electrode across the opening from the LOP of the end down to a shoulder 21 formed in the recess 17.

I provide my furnace with knock-down side walls formed by refractory bricks or blocks 22, laid upon each other and resting on the brick upon the side ledges 8 of the cradles. These bricks 22 are piled loosely to the level of the ends, and-having bedded in the electrodes in the manner described, the assembled furnace thus provides a refractory bottom and sides open overhead and having concrete end 'alls faced, where exposed to the heat, with the refractory composition lining 19. into the furnace space thus provided is introduced the charge 23 of sand, sawdust and coke, tnere being provided a spe cial conductor column of coke extending through thecenter of the stock concentric with and at each end contacting with the electrodes.

in 5 1 illustrate a conventional electrode holder section 18, two of which are clamped together about each electrode by means of the bolts passing through suitable openings which miss the water channels provided in each holder section. These water channels have their ends tapped for connection therewith of water circulation pipes and the outer bolts 2% serve to clamp to the holders condu tor bars 25 which are suitably connected up in an electric circuit. W nter is admitted by a. pipe 26 through rubber hose branches to one end of the holder sections on the left hand electrode (Fig. 2}, and after flowing through the holder the water is conducted by manifold hose pipe 2'? to the adjacent copper tube 12 through wh ch it flows to the right hand end of the furnace and thence passes by 'inanifold pipe 28 through the sections of the right hand electrode holder and thence by n anifold pipe 529 to theother copper tube 12, whence it flows back through the furnace to the dischar e hose 5 and thus corn ietes a circuit through the i The current for the furnace is celivered assen from the supply line 31 through conductors 32 to the conductors 25 on each holder section of the'left hand electrode (Fig. 2), and the current flows through the electrode and through the conducting core in the charge to the right hand electrode and thence passes out to the right hand conductors 25, and thence by conductors 38 to the tubes 12 through which it returns and completes the connection. through conductors 34 to the other supply line 35.

In operation, when the furnace has been charged as described and the water and electrical circuits connected up in the manner above pointed out, as the smelting operation proceeds the furnace shell will be subjected to excessive temperatures and will be substantially expanded both laterally and iongitudinally. Its lateral expansion is effectively resisted by the reinforced concrete cradles but its longitudinal expansion is left free and is absorbed by an endwise movement of the ends 1 on their supports 2. Obviously, the ends 1, being unconnected to the copper tubes, are entirely free of any physical connect-ion whatever either to each other or to the intermediate portion of the furnace. As the furnace chills the ends will not be retracted but any crack left between the ends and the intermediate portion of the furnace will become filled with stock and give no trouble. in practice, after several heats the movement of the ends is negligible. After the silicon. carbide is produced, the current is shut off, the side bricks 22 are torn down and removed and the mass in the furnace allowed a suitable period to cool after which it is removed from the furnace hearth and treated in the usual manner. The side wall bricks 522 are thereupon relaid and the operation can be repeated.

Though have described with great particularity the details of the embodiment of the invention herein shown, it is not to be construed that i am limited thereto, as changes in arrangement and' substitution of equi alents may be made by those skilled in the art without departing from the invention as defined in the appended claims.

Having thus described my invention, what claim new and desire to secure by Letters Patent, is:

1. An electric furnace of the character described, comprising a hearth, spaced concrete supports for said hearth, and concrete end walls for the furnace free of. fired connection to the hearth supports.

2. An electric furnace of the character described, comprising a furnace bottom, concrete bottom supports, and concreate end walls recessed to receive the electrodes and mounted free of rigid connection to furnace bottom or its supports.

3. An electric furnace of the character described, comprising a {furnace bottom having a plurality of spaced concrete bottom supports, detached concrete furnace ends,

and copper cooling tubes traversing the botspaced substantially U-shaped concrete cra-- dles supporting the bottom, and concrete electrode-supporting end walls.

6. An electric furnace of the character described, comprising a bottom, spaced substantially U-shaped concrete cradles adapted to support the bottom and having their tops.

forming side ledges, refractory blocks loosely laid on said side ledges to form knock-down side walls for the furnace, and end electrode supporting walls.

7. An electric furnace of the character described having monolithic end walls, slides upon which said walls are mounted free to move responsive to expansion of the interposed furnace walls.

8. An electric furnace of the character described, comprising a body portion formed of a bottom havin concrete supports, and side walls of loose blocks adapted to be torn down, i combination with monolithic end walls ad rails disposed lengthwise of the furnace and adapted to support said end free to slide thereon.

9. An electric furnace of the character described, comprising a body portion formed of a bottom having concrete supports, and side walls of loose blocks adapted to be torn down, in combination with monolithic end walls mounted free to slide lengthwise of the furnace, water-cooled electric conductors extending lengthwise through the furnace and passing loosely through and beyond the end walls, and. electrodes mounted in the ends and having electrical connections comprising a return circuit through said conductors.

10. In an electric furnace of the character described, the combination with the main body .portion of the furnace, of detached monolithic end walls tapering from their bases upwardly.

' 11. In an electric furnace of the character described, the combination with the main body portion of the furnace, of detached monolithic end walls having their outer endwall and their side walls inclined to produce a taper from their bases upwardly, said ends being adapted to support electrodes.

12. In an, electric furnace of the character described, the combination with the mainbody port-ion of the furnace, of detached monolithic end walls tapering from the sides and outer ends of their bases and having electrode seats, said walls having their inner faces recessed where exposed to the direct heat of the furnace, and a refractory composition mounted therein about the electrodes.

13. In an electric furnace of the character described, a'main furnace body, monolithic end walls mounted free to move apart and having an upwardly tapering shape with a central opening adapted to receive an electrode, there being a recess on the inner side of each end-adapted to receive a composition filler surrounding the electrode.

14. In an electrode furnace of the character described, a main furnace body, monolithic end walls mounted free to move apart and having. an upwardly tapering shape with a central opening adapted to receive the electrode and with a recess on the inner side to receive a composition filler surrounding the electrode, water-cooled tubes extending through the furnace body and projecting loosely through the ends, and electric circuits for the furnace including said copper tubes.

15. An electricfurnace of the character described, comprising end electrode supports, water-cooled electrode holders, copper cooling tubes extending lengthwise through the furnace on each side, connections partly at least of non-conducting material for conducting the water in circuit through the electrode holders and tubes, and an electric circuit including the electrodes and the furnace charge and said copper tubes.

In testimony whereof I affix my signature.

HAROLD E. l/VHITE. 

